Authorities launched a criminal investigation into the death of a 20-year-old inmate Tuesday at the Elmwood Correctional Facility.

Shortly after 4 p.m., the inmate’s cellmate reported that the man was unresponsive, said Santa Clara County jail spokeman Mark Cursi.

Cursi said correctional officers attempted cardiopulmonary resuscitation but failed to revive the inmate, who was still in his bed. He was declared dead at the scene, and there is no apparent cause of death.

The inmate, whose name was not released, was awaiting trial on undisclosed felony charges and was being held in medium security.

Sandra Gonzales is the deputy metro editor at the Mercury News, overseeing local news coverage. Previously, she was night city editor and has spent most of her journalism career as a reporter, covering a wide-range of beats: education, city government, courts and crime.